I had this same problem recently. While vacationing in an area of poor Sprint coverage I set my phone to "Roam only" to save battery, but most incoming calls went straight to voicemail. Very frustrating.

"If you think a weakness can be turned into a strength, I hate to tell you this, but that's another weakness."- Jack Handey

I have been using roam only for a while now, and I just realized all my calls go straight to voicemail. after playing phone tag all day, I decided to test it when I got home, put it in roam only, and called from my house phone, it went straight to voicemail... this sucks because i need this patch while at work!